This invention relates to part circle gear driven rotary irrigation sprinklers, and more particularly, to a new and improved biasing spring for biasing the gear train of such sprinklers into one or the other of two positions for rotating the sprinkler nozzle in the forward or reverse directions.
Part circle gear driven rotary sprinklers have long been known and used in the irrigation field. For example, the following United States Patents disclose such sprinklers and/or the drive mechanisms therefore: U.S. Pat. Nos. 3,107,056; 3,713,584; 3,724,757; 4,568,024; 4,708,291; 4,718,605; 4,901,924; 4,948,052; 4,955,542; and 5,086,977. The present invention relates specifically to a new and improved biasing spring usable with sprinklers of the types disclosed in the above-mentioned patents, the disclosures of which are incorporated herein by this reference.
While specific reference to these prior art patents can be made for details of construction for the design and operation of part circle, gear driven rotary sprinklers of the general types which the present invention is usable, such sprinklers typically include a generally cylindrical stationary housing within which is mounted a water driven motor, such as a water turbine or impeller, the output of which is directed to a reversing gear train drivingly coupled to a sprinkler nozzle rotatably mounted adjacent the upper end of the sprinkler housing. The reversing gear train operates to drive the sprinkler nozzle in alternating opposite rotary directions between preselected arcuate limits so as to irrigate a selected arcuate area around the sprinkler housing. Typically, the arcuate limits of nozzle rotation can be selected through the use of adjustable trip tabs which function to effect movement of the reversing gear train between a first position wherein the gear train drives the nozzle in a clockwise direction, and a second position wherein the gear train drives the nozzle in a counter clockwise direction.
The trip tabs engage a trip lever or arm rotatably supported by a trip collar mounted within the sprinkler housing, and the trip lever operates through a lost motion connection to engage a yoke plate forming a gear carrier support for the drive gear train. Shifting of the yoke by the trip lever causes the gear carrier to move between a first position where one terminal gear of the gear train engages a ring gear coupled to the sprinkler nozzle so that the nozzle is rotated in a clockwise direction, and a second position where another terminal gear of the gear train engages the ring gear to rotate the nozzle in the opposite, counter clockwise direction. To effect a snap-action of the yoke by the trip lever during sprinkler reversal, one or more over-center biasing springs are employed, typically acting between the trip collar and the sprinkler housing, as shown for example in U.S. Pat. Nos. 3,107,056 and 4,568,024, or between the trip collar and gear carrier, as shown for example in U.S. Pat. No. 4,955,542, or between the trip collar and housing and between the gear carrier and housing, as shown, for example in U.S. Pat. No. 4,718,605. In any case, the over-center biasing spring or springs act to convert the lost motion connection between the yoke and trip collar into a positive snap action of the gear carrier to bias and maintain one or the other of the terminal gears in driving relation with the ring gear.
As disclosed in the prior art patents mentioned above, the typical over-center biasing spring used with such sprinklers is formed from a generally flat, ribbon shaped metal, typically stainless steel, bent to have a shape generally like that of the Greek letter Nomegam with an arcuate head section and oppositely extending generally straight leg sections terminating in out turned ends, the out turned ends of each leg section being releasably engaged with a suitable seat which permits the spring end to pivot. Such springs are generally referred to as "omega springs." During a reversing operation, the spring seats are moved arcuately past each other causing one end of the omega spring to pivot past the other end. This causes the spring head and leg sections to deform and compress as the leg sections move toward each other, and once the leg sections have passed the over-center position, the stored energy of the compressed and deformed head and leg sections causes the leg sections to rapidly expand away from each other, thereby to effectively snap to the new extended position. For further details of this over-center snap action, reference can be made to the above mentioned patents.
During the normal life expectancy of a part circle gear driven sprinkler of the type with which this invention is primarily concerned, it is not uncommon that the reversing mechanisms may be required to operate several hundred thousand times. It has been found that with prior art omega springs of the aforementioned type, premature failure often occurs in the head section of the spring before the full life expectancy of the sprinkler has been reached. This can be attributed to spring metal fatigue caused by the cyclical stress experienced in the head section of the Omega spring during repeated deflections with prior art over-center Omega springs, much of the stress created during spring deflection is concentrated in the head section of the spring, with relatively lower stress levels occurring in the leg sections.
Another difficulty which has been found with such prior art biasing omega springs is that vibrations and shock loads sometimes found in pop-up type part circle gear driven sprinklers can cause the ends of the legs of the spring to disengage f rom their seats. In typical prior art Omega springs, the ends of the spring legs are provided with serrations and rely upon spring compression between the seats to maintain the spring in place by friction. As the repeated oscillations of the sprinkler fatigue the Omega spring, the frictional engagement of the spring legs against their seats decreases, thereby permitting the spring to become disengaged and render the sprinkler reversing mechanism inoperative. Further, during assembly of such prior art Omega springs, the spring must be manually compressed and installed in their seat. It is not uncommon that during installation, the prior art omega spring may be inadvertently overly compressed to a point at which permanent spring deformation occurs. This has also been found to reduce the useful life of the spring and result in premature spring failure.
Thus, there exists a need for an over-center biasing spring of the omega spring type for use with part circle gear driven sprinklers of the aforementioned general type and which will effectively eliminate premature spring failures and insure that the spring does not become disengaged from its spring seats during operation of the sprinkler over its full expected life. As will become more apparent hereinafter, the present invention has solved this need in a novel and unobvious manner.